1. Field of the Invention
The present invention generally relates to apparatus for reproducing an information signal and, more particularly, is directed to an apparatus for reproducing a video signal with a pulse code modulated (PCM) audio signal.
2. Description of the Prior Art
The Betacam (registered trademark) video tape recorder (VTR) employs a tape guide drum assembly in which two pair of close together rotary magnetic heads are mounted on a rotary head drum with an angular spacing of substantially 180 degrees between the two pairs of heads and records a frequency-modulated (FM) luminance signal and chroma signals on a magnetic tape by means of the two pairs of close together rotary magnetic heads so as to form respective slant tracks.
In the Betacam SP type video tape recorder, as shown in FIG. 1, of the 2 channel audio tracks CH1, CH2 formed along one side edge of a magnetic tape 1 by the Betacam video tape recorder, the inside audio track CH1 is sacrificed for the recording therein of PCM audio signals PA.sub.1, PA.sub.2, PB.sub.1, PB.sub.2, . . . along extensions of the respective slant tracks in which the FM-modulated luminance and chroma signals YA, CA, YB, CB, . . . are recorded. Further, in FIG. 1, reference symbol TC represents a time code track formed along the side edge of the magnetic tape 1 remote from the tracks CH.sub.1 and CH.sub.2.
A playback operation of Betacam and Betacam SP type video tape recorders will now be described with reference to FIGS. 2A-2K and, in order to facilitate such description, it will be assumed that the Betacam and Betacam SP type video tape recorders employ a tape guide drum assembly in which a single pair of rotary magnetic heads are mounted on a rotary head drum with an angular spacing of substantially 180 degrees between the heads.
According to the Betacam video tape recorder, in the normal playback mode (i.e., the magnetic tape is transported at the same speed as for the recording mode), the signals reproduced by the pair of rotary magnetic heads are comprised of alternately reproduced, high frequency video signals RFV-A, RFV-B, each representing one field, as shown in FIGS. 2A, 2B. These high frequency video signals are supplied to a head change-over switch (not shown), in which they are switched by a switching signal shown in FIG. 2C to provide a continuous signal of high frequency video signals RFV-A, RFV-B alternating at every field, as shown in FIG. 2D.
According to the Betacam SP type video tape recorder, in the normal playback mode (i.e., the magnetic tape is transported at the same speed as for the recording mode), the reproduced signals by the pair of rotary magnetic are comprised of heads, a high frequency video signal RFV-A for one field and a related PCM audio signal PCM-A and a high frequency video signal RFV-B for another field and a related PCM audio signal PCM-B, as shown in FIGS. 2E, 2F when the reproduced signals are supplied to the head change-over switch, which is switched by the switching signal shown in FIG. 2C, the PCM audio signals PCM-A and PCM-B are dropped to provide a continuous signal of the high frequency video signals RFV-A, RFV-B for alternating fields, as shown in FIG. 2D similarly to the Betacam video tape recorder.
However, in the Betacam SP type video tape recorder, in the variable tape speed playback mode, a problem arises which will be explained with reference to the -1 time normal tape speed playback mode (that is, the playback mode in which the magnetic tape is transported at a speed -1 times the transport speed for the recording mode).
In the -1 times normal tape speed playback mode, the signals reproduced by the pair of rotary magnetic heads, that is, the high frequency video signals RFV-A, RFV-B for odd and even fields and the related PCM audio signals PCM-A, PCM-B are reproduced in reduced times, as shown in FIGS. 2G, 2H, while the timing of the switching pulse (see FIG. 2I) is constant regardless of the change of the transport speed of the magnetic tape. As a consequence, when the signals shown on FIGS. 2G and 2H to be reproduced by the pair of rotary magnetic heads, respectively, are supplied to and switched by the change-over switch, then the output of the change-over switch is composed of at least portions of audio signals PCM-A, PCM-B, as shown in FIG. 2J. Accordingly, if the output signal shown in FIG. 2J is FM-demodulated, then video signals V-A, V-B and a synchronizing (sync.) signal are obtained along with portions of the PCM audio signals PCM-A, PCM-B which are reproduced as large noises N, as shown in FIG. 2K.